Update to 15.0.1

Changelog:
    FIXED Sites visited while in Private Browsing mode could be found through manual browser cache inspection (787743)
    NEW Silent, background updates
    NEW Support for SPDY networking protocol v3
    NEW WebGL enhancements, including compressed textures for better performance
    NEW Localization in Maithili (see all available locales)
    CHANGED Optimized memory usage for add-ons
    DEVELOPER JavaScript debugger integrated into developer tools
    DEVELOPER New layout view added to Inspector
    DEVELOPER High precision event timer implemented
    DEVELOPER The CSS word-break property has been implemented.
    DEVELOPER New responsive design tool allows web developers to switch between desktop and mobile views of sites
    HTML5 Native support for the Opus audio codec added
    HTML5 The <audio> and <video> elements now support the played attribute
    HTML5 The <source> element now supports the media attribute
    FIXED Focus rings keep growing when repeatedly tabbing through elements (720987)

(ryoon)